1. Field of the Invention
This invention relates to a rolling-bearing unit for wheel support for supporting an automobile wheel such that it rotates freely with respect to the suspension.
2. Description of the Related Art
A rolling-bearing unit for wheel support is used for supporting automobile wheels such that they rotate freely with respect to the suspension. FIG. 6 shows a first example of a rolling-bearing unit for wheel support that was previously considered for this purpose. This rolling-bearing for wheel support comprises an outer-race 1, a hub 2 and a plurality of rolling elements 3a, 3b. Of these, the outer-race 1 has a double row of outer-ring raceways 4a, 4b formed around its inner peripheral surface and an installation section 5 formed around its outer peripheral surface for fastening to the suspension. Moreover, the hub 2 is located radially on the inside of the outer-race 1 such that it is concentric with the outer-race 1.
There is a flange 6 formed around the outer peripheral surface on the outside end (This is the outside end in the axial direction which is on the outside in the width direction of the vehicle when the bearing is installed in the automobile, and is the left end in the figures.) of this hub 2 for supporting and fastening to the wheel, and a double row of inner-ring raceways 7a, 7b are formed around its outer peripheral surface. In addition, there is a plurality of rolling elements 3 between the inner-ring raceways 7a, 7b and the outer-ring raceways 4a, 4b, and they are held in place by synthetic resin or metallic retainers 8 such that they rotate freely.
The construction shown in FIG. 6 and FIG. 7 is provided for supporting a wheel of a relatively heavy vehicle, so tapered rollers are used as the rolling elements 3a, 3b, and the cross-sectional shape of the outer-ring raceways 4a, 4b and the inner-ring raceways 7a, 7b is formed in a straight manner.
Moreover, the hub 2 is formed by combining a hub body 9 and a pair of inner-races 10a, 10b, and the aforementioned inner-ring raceways 7a, 7b are formed around the outer peripheral surface of these inner-races 10a, 10b. In order to combine the hub body 9 with the pair of inner-races 10a, 10b, a support step section 11 is formed around the outer peripheral surface of the hub body 9 from the middle to the inside end (This is the inside end in the axial direction which is the end toward the middle in the width direction of the vehicle when the bearing is installed in the automobile, and is the right end in the figures.). The pair of inner-races 10a, 10b is tightly fitted around (pressure fitted) around this support step section 11 through interference fit. Furthermore, a crimped section 13 that is formed by plastically deforming a cylindrical section 12 is formed on the inside end of the hub body 9, and the inside end surface of the inner-race 10b on the axial inside is retained by the crimped section 13. A step section 14 is located on the outside end of the support step section 11, and by holding the pair of inner-races 10a, 10b between the crimped section 13 and the step section 14, the inner-races 10a, 10b are fastened to the hub body 9. Also, with the inside end of the inner-race 10b held by the crimped section 13, a pre-load is applied to the bearing section comprising the rolling elements 3 and raceways 4, 7. Construction, in which the technique of holding the inside end of the inner-race with a crimped section is applied to a tapered roller bearing, is disclosed, for example, in International Patent Publication WO 98/58762.
As shown in FIG. 7, for the rolling-bearing unit for wheel support that is the object of this invention, the inner-ring raceway 7a may also be formed directly around the outer peripheral surface in the middle section of the hub body 9 of the hub 2. In this case, a support step section 11 on which one inner-race 10b is fitted and fixed is formed on only the inside end of the outer peripheral surface of the hub body 9, and a step section 14a for coming in contact with the outside end of this inner-race 10b is formed on the hub body 9 itself.
It will be noted that in the case of the pair of inner-races 10a, 10b shown in FIG. 6, the surface of the inside end of the outside inner-race 10a corresponds to the aforementioned step section 14a. 
Moreover, in the example shown in the figures, there is a spline hole 15 formed in the center of the hub body 9 of the rolling-bearing unit for supporting the drive wheels. Furthermore, there are seal rings (assembled seal rings) 16a, 16b between the inner peripheral surface on both ends of the outer-race 1 and the inner-races 10a, 10b, and they cover the openings on both ends of the space 17 where the rolling elements 3a, 3b are located.
In the case of the second example shown in FIG. 7, the seal ring 16a, which covers between the outside end of the outer-race 1 and the middle section of the hub 2, is fitted around the outside end of the outer-race 1.
When a rolling-bearing unit for wheel support that is constructed in this way is installed in an automobile, the aforementioned installation section 5 is connected to and fastened to a knuckle or the like of the suspension, and fastens a wheel to the flange 6. In this way, the wheel is supported such that it rotates freely. Also, a spline shaft that is an accessory of a constant-velocity joint (not shown in the figure) is inserted in the spline hole 15 such that the wheel can be rotated and driven freely by way of the hub body 9.
A technique for simplifying the work of forming the crimped section 13 for fastening the inner-races 10a, 10b to the hub body 9, where the inner-races 10a, 10b are fitted around the outer peripheral surface of the hub body 9, is disclosed in West German Patent No. DE3418440A1, and is shown in FIG. 8 and FIG. 9. In the case of the construction disclosed in this disclosure, in order to form the crimped section 13 for retaining the surface on the inside end of the inner-race 10b, concave grooves 18a, 18b are formed in the circumferential direction around the inner and outer peripheral surfaces on the outside end of the cylindrical section 12 that is formed on the inside end of the hub body 9. Of these, the concave groove 18b that is formed around the outer peripheral surface of the outside end of the cylindrical section 12, is a small-diameter section as explained later. Since the concave grooves 18a, 18b are formed to reduce the thickness of the cylindrical section 12, which becomes the bent section when forming the crimped section 13, it is easy for the cylindrical section 12 to deform plastically. Therefore, it is possible perform processing of the crimped section 13 without heating the cylindrical section 12.
The construction shown in FIG. 8 and FIG. 9 is for supporting the wheel of a relatively lightweight automobile, so balls are used as the rolling elements 3a, 3b, and the cross-sectional shapes of the outer-ring raceways 4a, 4b and inner-ring raceways 7a, 7b are formed in an arc-shape manner.
In the case of the prior art construction shown in FIG. 6 and FIG. 7, the relationship between the diameter of the inner-ring raceway 7a, 7b that is formed around the outer peripheral surface of the inside inner-race 10b and the diameter of the crimped section 13 is not particularly regulated, so it was difficult to maintain durability as well as reduce the size and weight. The reason for this is as follows. A large outward axial load is applied to the surface on the inside end of the inner-race 10b when forming the crimped section 13. In addition, when this axial load is applied to the large-diameter-side collar 27 that is formed around the outer peripheral surface on the inside end of the inner-race 10b, a moment load is applied to the base (inner-diameter-side end) of this large-diameter-side collar 27 in the direction that causes a portion of this large-diameter-side collar 27 near the outer periphery to displace axially outward. On the other hand, in order to prevent interference with the grind stone when finishing the outside surface of the large-diameter-side collar 27 and inner-ring raceway 7b, a grinding-relief groove 28, as shown in FIG. 10, is formed in the section that connects the surface on the outside end of this large-diameter-side collar 27 with the inner-ring raceway 7b. Therefore, when a moment load is applied to the large-diameter-side collar 27, stress is concentrated at this grinding-relief groove 28, making it easy for damage such as cracking to occur in this section.
Conventionally, in order to prevent damage from occurring due to this reason, the thickness in the axial direction of the large-diameter-side collar 27 was made sufficiently large in order to suppress elastic deformation of the large-diameter-side collar 27 regardless of the aforementioned moment load, and to keep the stress applied to the grinding-relief groove 28 at a minimum. Therefore, the length dimension in the axial direction of the inner-race 10b having the aforementioned large-diameter-side collar 27 was increased more than required for as a component for a rolling-bearing unit for wheel support, and thus the dimension in the axial direction of the rolling-bearing unit for wheel support was increased by that amount, making it difficult to make the bearing unit more compact and lightweight.
In the case of the prior construction shown in FIG. 8 and FIG. 9, the inventors found through testing that a large load was applied outward in the radial direction to the inside end of the inner-race 10c when forming the crimped section 13 by plastically deforming the cylindrical section 12 outward in the radial direction. The reason for this will be explained using FIG. 8, FIG. 9 and FIG. 11.
As shown in FIG. 8 and FIG. 9, when the cylindrical section 12 on which a concave groove 18b is formed around the outer peripheral surface of its outside end (base end) is deformed plastically outward in the radial direction, a protrusion 19 as shown in FIG. 11 is formed in the section corresponding to the outside edge (starting point) of the concave groove 18b on the outer peripheral surface of the cylindrical section 12. It should be noted that FIG. 11 shows the axial direction (left and right direction in FIG. 11) at a magnification rate of about 10xc3x97, and shows the radial direction (up and down direction in FIG. 11) at a magnification rate of about 1000xc3x97. In the case of a general rolling-bearing unit for wheel support of an automobile, the width W19 of the protrusion 19 is about 0.1 to 0.2 mm, and the height H19 of the protrusion 19 is about 0.001 to 0.10 mm.
On the other hand, in the case of the prior art shown in FIG. 8 and FIG. 9, the outside edge of the concave groove 18b faces the cylindrical section 12, which is a section on the inner peripheral surface of the inner-race 10b, and the inner diameter of which does not change with respect to the axial direction. Therefore, before forming the crimped section 13, the outside edge of the concave groove 18b comes in close contact with the inner peripheral surface of the inner-race 10b. When forming the crimped section 13a from this state by plastically deforming the cylindrical section 12 outward in the radial direction, the protrusion 19 strongly presses the inner peripheral surface on the inside end of the inner-race 10b outward in the radial direction, and plastically deforms the inside end of this inner-race 10b outward in the radial direction although a little. Also, in the case of elastic deformation, the cross-sectional shape or diameter of the inner-ring raceway 7b that is formed around the outer peripheral surface of the inner-race 10b, changes a little from the desired one, and there is a possibility that the pre-load applied to the rolling elements 3a, 3b will be a little off from the proper value.
Furthermore, in the case that the prior art shown in FIG. 8 and FIG. 9 is applied to a rolling-bearing unit for wheel support that is a double-row tapered roller bearing unit as shown in FIG. 6 and FIG. 7, the crowning that is performed on the inner-ring raceway 7b around the outer peripheral surface of the inside inner-race 10b is either reduced or lost, which results in the possibility of edge loading occurring on part of the contact area between the inner-ring raceway 7b and the rolling contact surface of each rolling element 3b. In other words, since the crowning that was performed for preventing the occurrence of edge loading of the inner-ring raceway 7b is lost, prevention of edge loading become uncertain. That is, of the crowning performed on the inner-ring raceway 7b, the crowning amount performed on near the inside end in the axial direction is decreased or lost. As a result, it becomes easy for high surface pressure due to edge loading to be applied at the area of contact between the inside end of the inner-ring raceway 7b and the inside end of the rolling contact surface of each rolling element 3b. The high surface pressure due to this kind of edge loading is a cause of shortened rolling fatigue life of the inner-ring raceway 7b and is not desirable.
The rolling-bearing unit for wheel support of this invention was invented by taking the problems described above into consideration.
An object of the present invention is to provide a rolling-bearing unit for wheel support wherein by making it impossible for a moment load to be applied to this large-diameter-side collar 27 when processing the crimped section 13, it is possible to keep the thickness of the large-diameter-side collar 27 and the length dimension of the inner-race 10b to that which is basically required for components of a rolling-bearing unit for wheel support, and thus it is easier to make the rolling-bearing unit for wheel support more compact and lightweight.
Another objective of this invention is to make it easier to construct a rolling-bearing unit for wheel support that is more compact and lightweight by not applying a moment load to the large-diameter-side collar 27 when processing the aforementioned crimped section 13.